Oscillation generator



Patented Mar. 1, 1932 UNITED STATES PATENT OFFICE 'WARREN' A, HARRISON, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN' III'JETC- TIBIC` COMPANY, INCORPORATED, 0F "NEW YORK, N. Y., A CORPORATION 0F NEW YORK oscrLLA'rIoN GENERATOR Application led August 5, 1924. Serial No. 780,165.

erators and more particularly to generators having means for maintaining substantially constant the frequency of osclllations.l

It is known that piezo electric devices may be used to control the frequency of oscillations generated by space discharge tube oscillators. The crystals used for controlling high frequency oscillators are frequently cut from quartz and it is found that they will respond Jto a number of frequencies with varying degreesof activity. Thereis usually one natural frequency at which the crystal gives the greatest response and in general, oscillators, the circuits of which include piezo electric devices, produce oscillations of a single frequency determined solely by the natural frequency of the crystal. It has been customary in the past to cut the piezo crystals used in oscillation generators from quartz so that the dimension in the direction of the axis of vibration of the crystal is small as compared to the other dimensions.

.It is found that crystals so cut have a number of frequencies in the same neighborhood to which they respond to a substantially equal degree. When crystals of this character are employed for controlling the frequency of oscillation generators it is practically impossible to predict at which one of these neighboring frequencies oscillations will take place. The eiciency and otherfactors of theoscillator circuit at different frequencies have a considerable influence in determining the frequency of oscillations. Because of this difficulty of accurately predicting the frequency of the oscillations produced by an oscillator using a piezo electric control element as heretofore proposed, their application has been limited, in spite of the fact that oscillators Ahaving such control elements possess the great advantage that they generate oscillations of substantially constant frequency.

An object of the present invention is to control within narrow limits, the frequency of oscillations generated by an oscillator of this type.

Another object is to control the generation of electrical oscillations at any one of a plurality of frequencies.

A specic object is to selectively control the frequency ofgenerated oscillations in accordance with any one of the natural frequencies of a plurality of piezo electric devices.

capacity between electrodes of a space discharge tube, arranged to produce oscillations at desired frequencies, to prevent the production ofl oscillations of undesired frequencies.

An additional object is to control the feedback of energy from the output circuit to the lcapacityT of the tube, whereby the generation of oscillations of undesired frequencies is prevented.

A still crystal controlled oscillator wherein the crystal used is designed to have dimensions such that its response to some particularfrequencies is substantially greater than its response to other` closely adjacent frequencies.

An additional feature relates to an oscillation generator having means for selecting any one of a plurality of natural frequencies of a piezo electric control element.

In its more general aspects, the invention comprises an oscillation generating system including an amplifying element arranged in a regenerative circuit and a frequency control element coupled thereto. The frequency control elementmay-preferably consist of a plurality of component parts. At least one of the component parts of the control element is included in the feed-back portion of the regenerative system. This part preferably is arrangedto have an electrical reactancc that is substantially equivalent to the reactance i11- llerent in certain other portions of the system whereby a balance is maintained at certain frequencies to prevent the establishment of A further object is to compensate for the' further feature relates to a piezo parasitic or undesired oscillations. The component part just mentioned is arranged to cooperate with an additi al part of the frequency control elemen or determining at which one of a plurality of possible frequencies the system will operate. Oscillations are generated in the system at desired frequencies by virtue .of the fact that the reactance of the first mentioned component part of the frequency control element, which balances the reactance of other portions of the system, falls approximately to zero at the desired frequency. This component element which, for example, may be a piezo electricv device is preferably sharpl resonant so ss to maintain the frequency o oscillations substantially constant within very narrow limits.

The invention, both as to its organization and method of operation as well as the further objects, features and advantages thereof, will be more clearly understood by reference to the following description read in connection with the accompanying drawings in which:

Fig. 1 illustrates a piezo crystal controlled oscillator.

Fig. 2 illustrates an oscillator similar to that of Fig. 1 having an amplifier coupled to its output circuit.

Fig. 3, illustrates an oscillator similar to that of Fig. 1 having an amplifier coupled thereto by means of a two-winding transformer. l

Figs. 4 and 5 illustrate a section of a quartz crystal showing the manner of cutting a piezo electric crystal therefrom.

The oscillator illustrated in Fig. 1 comprises a space discharge tube of the three-electrode type having an input circuit 11, an output circuit 12, and a feed-back circuit 13.

, The input circuit is connected to the control electrode and cathode of the tube and includes a resonant circuit comprising an adjustable condenser 14, in parallel with the inductance coil 15. A lead connecting the mid-point of coil 15 to the cathode of tube,` 10 includes a ,battery 16 that is provided to supply a suitable average polarizing potential to the tube control electrode.

One terminal of the inductance v15 is con -i nected to the control electrode, the opposite terminal is connected tothe feed-back circuit 13. The latter includes a coupling device il-` lustrated as a piezo electric element 17.

Space current is supplied to the tube by means of a battery 18 in series with an impedance 19. Output leads 20 and 21 are arranged to be connected to a load device such for example as an amplifier, modulator or wire line. Lead 20 includes a blocking condenser 22 to prevent the passage of direct current from battery 18 into the load circuit. The cathode of tube 10 is heated by a source of current illustrated as a battery 23 in series with a resistance 24.

i Condenser 25,*shown in dotted lines, represents the inherent capacity between the control electrode and anode of tube 10 includindicated in Fig. 4. The plates 26 are placed adjacent to the sides A and B, Fig. 4, of the parallelopiped. Itis a well known property of crystals so cut that, when subjected to physical stress in the direction of the dotted axis, plus and minus .charges appear on the faces A and B and when subjected to an electrostatic field on the faces A and B it undergoes physical deformation along the dotted axis. The signs of the charges produced in the first case depend upon the character of the stress, that is, whether tension or compression, whereas in the second case the physical deformation, i. e., elongation or contraction under the action of an electrostatic field, depends upon the direction of the field.

If the stress changes from compression to tension or vice versa, the signs of the electric charges on the faces A and B are reversed, whereas if the electrostatic field is alternately reversed the crystalundergoes alternate elongation and contraction in the direction of the dotted axis, or in other words the crystal vibrates.

The crystal 27 is preferably cut as illustrated in Figs. 4 and 5 with its dimension in the direction of the axis of vibration, namely the dotted axis of Fig. 4, of the same order as its other dimensions. It is found that a crystal of such proportions has a plural-ity of natural frequencies but that its response to the fundamental frequency is substantially greater than its response to other frequencies which moreover are not in the samev neighborhood.

An advantage of the present invention lies one of the natural frequencies of the piezo electric device at which it is desired togenerate oscillations and to prevent the production of oscillations corresponding to any other of its natural frequencies. This advantage constitutes a material improvement lover any of the crystal control-led oscillators hitherto known.

The piezo electric device may be considered as a reactance which is high at frequencies other than those to which the crystal responds but is quite low or substantially zero at the resonant frequencies. This reactance property of the crystal may be utilized to explain the operation of the present invention.

The circuit of Fig. 1 operates to generate electrical oscillations by virtue of the feed back coupling supplied through the reactance of the piezo electric device 17. This is in the will be produced. At frequencies other than those to which the crystal is responsive, the

' eiiiciency of the circuit is so reduced that oscillations of these frequencies can not be generated. Preferably the capacity of the piezo electric device should normally be equal to that between the tube electrodes as indicated by the dotted condenser 25. For the frequencies at which the reactance of the piezo electric device 17 becomes very small or zero, the circuit is sufficiently efficient to maintain oscillations provided the tuned circuit 14-15 is adjusted, as just explained, to resonance approximately at one of these frequencies.

To increase the number of frequencies that may be generated in this circuit, other crystals such as crystal 17 that are responsive to frequencies different from those` to which the crystal 17 is responsive may be connected in parallel thereto. Again byadjusting condenser 14 to the proper value the oscillator may be caused to produce oscillations'at any desired one of the additional frequencies,

and the crystal then acts to confine the frequency of the oscillations produced, within very narrow limits to the selected value.

In one arrangement actually operated it was found that space discharge tubes having different characteristics could be used in the circuit, andthat the filament current and B battery potential could be changed without producing an appreciable efectupon the frequency of oscillations generated. Grounding and shielding of the circuit also produced a negligible frequency change.

In Fig. 2, the oscillator 28, which comprises space discharge tube 10, the resonant circuit 14-15 and the piezo electric device 17, may be identical with the oscillator of Fig. 1 although it is not illustrated as including the additional 17. This oscillator is impedance coupled to a space discharge tube amplifier 29. The amplifier 29 has an input circuit connectedfto its control electrode and cathode, which includes resistance 30 in series with battery 31. The space current circuit of the amplifier 29 includes impedance32. The filaments of tubes 10 and 29 are heated in parallel by a source 23. A source 18 supplies space current to both of these tubes.

`Output leads 20 and 21 are arranged to lsup-.

ply energy from amplier 29 to a load circuit. Blocking condenser 22 prevents cur .rent supplied by battery 18 from flowing in the input' circuit of amplifier 29. Condenser.

22 serves to block the iow of direct current from battery 18 through a load circuit connected `to leads 20 and 21.

In Fig. 3, a piezo electric crystal controlled oscillator 33 is coupled toa space discharge tube amplifier 34 by means of a two winding transformer 35'. The oscillator il- -lustrated in 'this gure corresponds to the oscillator in Figures 1 and 2 with the exception that the primary winding of transformer 35 replaces the resistance 19. The amplier 34 comprises a space discharge tube 36 having a tuned circuit connected in its input circuit which includesl the adjustable condenser 37 in parallel with the secondary winding of transformer 35. The mid-point of this winding is connected to the filament of tube 36. One outer terminal is connected to the control electrode of this tube and the opposite terminal is connected to the anode of .tube 36 in series with compensating condenser 38. This condenser is arranged to balance the grid-plate capacity of the tube vin order t0 prevent the production of para sitic oscillations in the amplifier circuit. Space 4current is supplied to tube 36 by battery-18 through a series resistance 39. Output leads`f20 and 21 are provided for connecting the amplifier to a load clrcuit which may be for example, another amplifier stage. Blocking condenser 22" serves thesa-me purpose as condensers 22 and 22 as 1n Flgures 1 and 2.'

In the circuits of Figs. 2 and 3, osclllations are supplied from the crystal controlled oscillators to the respective amplifiers from which they may be supplied to any desired load circuit connected to thc leads 2O and 21.

Obviously numerous modifications of the arrangements described above and involvmg the principles of this invention could be made without departing from lts spirlt and scope. Accordingly, the present disclosure being merely representative of certaln uses to which the invention may be applied, 1s given for the purpose of completely and clearly explaining the principles involved.

The invention therefore, is to be understood to be limited only by tle scope of the appended claims.

What is claimed is: Y

1. An oscillation generator which comprises a three electrode space discharge tube, inputand output circuits for said tube, and 'means coupling said circuits to control the generation of oscillations comprising a piezo electric device, having its capacity proportioned with respect to the capacity between certain electrodes of said tube and being connected in the circuit to balance such interelectrode capacity at all except desired oscillation frequencies, said piezoelectric device yserving as the principal frequency determining element at thedesired oscillation frequencies.

' 2. An oscillation generator which comprises a space discharge device, input and output circuits for said device, said circuit-s being coupled to cause the generation of oscillations, and means comprisinga piezo electric'device for determining the degree of .electrical coupling of said circuitsto enable the generation of oscillations of a plurality of frequencies, said piezo electric device being proportioned with respect to the capacity between certain electrodes of said discharge device and being connected tobalance the v at other than said cuit to balance the system against oscillations at all frequencies except those at which the piezo electric device oscillates.

4. In an oscillation generator, a three electrode space discharge device ,having input and output circuits, said circuits being cou'- pled by the natural capacity of their conductors, and balancing means for-said c ouy pling capacity for controllingthe generation 0f oscillations, said means having a capacity balancing the system against oscillations at some frequencies and substantially no reactance at other-frequencies, whereby at the latter mentioned frequencies oscillations are produced under control of said means.

' 5. An oscillation generator which comprises a three electrode space discharge devlce, an input circuit connected to two elec- 4trodes of said device, sa1d input circuit 1ncluding a resonant circuit, an output circuit for said device, a piezo electric device electrically coupling said input and output circuits and cooperating with said resonant circuit to perfect a balanced bridged circuit except when the circuit as a whole oscillates at a resonant frequency of said device so as to l determine the frequency of oscillations 'within narrow limits. l

6. An electric oscillator comprising a three electrode space discharge tube, input and output circuits for said tube, said circuits being coupled together and means also electrically coupling said circuits to normally prevent the generation of oscillations in'said oscillal tor, said means comprising a piezo elect-ric device having substantially zero reactance at desired frequencies to allow the generation of oscillations of these frequencies and having at other frequencies a capacity balancing theinter-electrode capacity of said space discharge device whereby the tendency of the i systemto produce oscillations at other thanv as to its capacity and connected in circuit to compensate for capacitylbetween said electrodes to prevent the generation of undesired oscillations.

8. An oscillation generator comprising a space discharge tube amplifier havinginherent capacity, a -frequency control element coupled to said amplifier, said control element having substantial reactance at undesied frequencies and substantially zero reactance at desired frequencies, and so positioned as to cause its reactance to balance the capacity .of said amplifier to thereby cause the generation of voscillations only at said desired frequencies. l v

V 9. An oscillation generator comprising an amplifying/ element including a three electrode space discharge tube, a frequency control elemen't, having a plurality of component parts, one part of said control element being al piezo-electric device having substantial reactance at undesired frequencies and substantially `zero reactance at a plurality'of desired frequencies, said device having its v capacity proportioned with respect to the capacity between electrodes of said tube and being connected to balance the system against oscillating at frequencies outside of certain definite ranges in -the vicinity ofthe frequencies at which said device has substantially zero reactance, and means to select one of said plurality `of desired frequencies at which oscillations shall be generated.

l0. An oscillation generator which com-- prises, an' amplifying element arranged in a regenerative system andhaving reactance tending to cause the production of oscillations, a frequency control element for determining the -frequency at which oscillations may be generated, said control element including a piezo crystal havin Aa dimension in the direction of the axis o vibration `of the same order 'as its other dimensions and capacity reactance proportioned with respect to the reactance of said amplifying element and connected to balance said'element against oscillating at selected frequencies.

l1. An oscillation producing system comprising a space 'discharge device having a cathode,ian anode and a grid or impedance controlling element, a piezo electric` device. a resonant circuit comprising inductance and capacity having its terminals connected across said anode and that said piezo electric device is included in series in the connection from said resonant grid elements except Y circuit to `one of said'two elements, the cathode being connected to a point in said inductance intermediate its ends, ,whereby said system oscillates at frequencies at which said ,5 piezo electric device exhibits characteristically low reactance, the capacity of said l `piezo electric device opposing the regenerative effects of interelectrode capacity of said discharge device at other than said frequencies, whereby oscillations at said other frequenciesare effectively prevented.

12. In a frequency control or stabilizing system a multiplicity of piezo .electric crystals .of different frequency` characteristics and means for selectively sustaining the oscillations of any one of said crystals at its characteristic frequency. p l f 13. In a frequency .control or staobilizing.

system a multiplicity ofpiezo electric' crystals of diEerent frequency characteristics, an electron tube circuit common to al1 of said crystals, and means connected with said electron tube circuit .for selectively sustaining the oscillations of any one of said crystals at its characteristic frequency.

14. In a frequency controlor stabilizing system a multiplicity of piezo electric crystals of different frequency characteristics, an electron tube circuit connected with said crystals.

and anadjustably tuned circuit connected with said electron tube circuit for selectively sustaining the oscillations of any one of said -fcrystals at its characteristic frequency.`

15. The combination of a piezo .electric of frequencies, and means for sustaining the vibrations at one of the frequencies, said crystal being so positioned withrelation to said means as to interpose a neutralizing reactive effect on said means for other frequencies than those at which thecrystal is capable of vibrating, so as to oppose vibrations at such other frequencies.

16. An oscillation generator comprising a space discharge tube, an input circuit and an output circuit for said space discharge tube,

said circuits beingv capacitatively coupled, aV

frequencies of said piezo electric device, so` as to prevent vibratlons at such other frequencies. a

17. In an electric wave transmission system comprising a piezo electric device having a vibrational crystal and electrodes, a'metliod of -selective transmission .which .comprises d transmitting energy of a range of frequencrystal capable of vibrating at af plurality cies through said device and neutralizing the components of the energy transmitted by virtue of the inter-electrode capacitance of the deviceV under static conditions.

18. In an electric wave transmission system,a piezo electric crystal resonator, a device having an inherent capacitance equal to the inter-electrode capacitance Alof said resonator under static conditions, and means to neutralize some of the components of the energy passed through the resonator by energy passedthrough the device.

19. In an electric wave transmission sys- 'tem, a plurality of piezo electric crystal resonators, a device having an inherent capacitance equal to the inter-electrode capacitances of all said resonators under static conditions, and means to neutralize `some of the components of the energy passed through said resonators by energy passed through said device.

2Q. In an electric wave transmission system, a piezo electric -crystal resonator, means` l to transmit energy through said resonator, and means to neutralize a component of said transmitted energy equal to the energy which would pass through said vresonator if it did not resonate.

21. In an electric wave transmission system, a piezo electric crystal resonator, means to transmit energy through said resonator,

and means to neutralize a component of said transmitted energy equal to the energy which would pass through a capacitance equal to the inter-electrode capacitance of said resonator when quiescent.

In witness' whereof, I hereunto subscribe my name this 29th day of July A. D., 1924.

WARREN A. MARRISON. 

